Aerobic/Anaerobic Respiration- Cellular metabolic process that coverts nutrients into energy and waste products. Aerobic respiration requires oxygen, anaerobic respiration does not. Anaerobic respiration dominates in low oxygen enviroments.
AVHRR - Advanced Very High Resolution Radiometer. An instrument carried aboard NOAA polar-orbiting satellites.
CASA - Carnegie-Ames-Stanford Approach. A terrestrial ecosystem model driven by satellite measures of vegetation greenness (NDVI). See Potter et al. .
CDIAC - The Carbon Dioxide Information and Analysis Center, a CO2 analysis program of the U.S. Department of Energy located at the Oak Ridge National Laboratory (ORNL).
CIRES - Cooperative Institute for Research in Environmental Sciences. A joint NOAA-University of Colorado, Boulder research institute.
Column Average - The average mole fraction of carbon dioxide in a vertical column of air starting at some point on the earth's surface and extending to the top of the atmosphere. This is a relevant quantity for comparison with satellite observations, and a vertical weighting function may be used to simulate the sensitivity of the satellite instrument or account for decreasing atmospheric pressure with altitude.
Covariance - Quantifies how much two parameters vary with each other. Parameters that vary perfectly together will have positive correlation of 1, while parameters that vary in opposition will have correlation of -1.
Data Assimilation - The process of constraining model predictions to be consistent with observations. Models express our understanding of basic physics and chemistry, but this grounding is often not sufficient to produce a realistic simulation. Observations inform us about the state of the atmosphere (chemical constituent, in the case of CarbonTracker) at one place and at one time, but do not by themselves tell us about other places and times. Data assimilation brings these together to yield a simulation that is as consistent as possible with both theory and with observations.
Dynamical Model - A prediction of parameters at future times based on parameters from previous times. A simple example of a dyanmical model is persistance, were parameters are assumed to be unchanged from on time step to the next.
EC - Environment Canada
ECMWF - The European Centre for Medium-Range Weather Forecasts. CarbonTracker uses the ECMWF operational "forecast" model for the meteorological drivers of the TM5 transport model.
EDGAR - Emission Database for Global Atmospheric Research. A fossil fuel emissions database. See EDGAR.
Emissions Inventories - In CarbonTracker, fossil fuel inputs of methane to the atmosphere are estimated from industry, EPA, and other governmental estimates of the production and consumption of coal, oil and natural gas. These are called "emissions inventories" for fossil fuels.
EnKF - Ensemble Kalman filter. An inversion scheme based on the classic Kalman filter algorithm. The EnKF uses the power of parallel computers by numerically representing the covariance matrix of parameter uncertainty with a large ensemble of slightly different realizations.
Ensemble - A randomly generated set of statistically plausible realizations of a state, for example the parameters estimated by CarbonTracker. Ensemble members are generated using estimated mean and probability distributions of parameters.
Enteric Fermentation - A digestive process in ruminants in which microorganisms help to convert carbohydrates into easily-digested substances. This process leads also produces methane.
ESRL - Earth System Research Laboratory. A NOAA laboratory in Boulder, Colorado.
EVI - Enhanced Vegetation Index. A satellite measure of vegetative greenness. A follow-on to the NDVI, but using the MODIS instrument instead of AVHRR.
Flux - The flow of mass across a surface, such as the interface between the land surface and the atmosphere. In CarbonTracker, we estimate the transfer of carbon mass between the land and the atmosphere, and the ocean and the atmosphere.
GFED2 - Global Fire Emissions Database, version 2. Refs: Randerson et al.  and Randerson et al. .
GMD - Global Monitoring Division. Part of the NOAA ESRL complex in Boulder, Colorado.
GPP - Gross primary production. Th amount of carbon fixed by plants during photosynthesis.
Hydraulic Fracturing - Injection of water and chemicals at high pressure underground to induce fracturing of shale rock so that embedded gas and oil may be extracted.
MBL - Marine boundary layer. Technically, the lowest level of the atmosphere over the ocean. Practically, this is an idealized construct of air representing the well-mixed lower atmosphere away from continental sources and sinks of atmospheric trace gases.
Methanogenesis - Anaerobic respiration process in which methane is produced. Methanogens belong to the group of organisms known as "Archaea".
Model-Data Mismatch Error - Measurement error that captures both measurement uncertainty and uncertainty in the ability of a transport model to adequately simulate the measurements. For atmospheric trace gas assimilations using in situ observations, the uncertainty associated with the transport model is much larger than the actual measurement uncertainty. The model-data mismatch error is difficult to quantify, yet it is important because a large value will reduce the influence of a particular measurement in the assimilation.
MODIS - Moderate-Resolution Imaging Spectroradiometer.
Mole Fraction - The mole fraction is defined as the number of molecules of an atmopsheric trace gas in any given air parcel divided by the total number of all molecules (except water) in that parcel. For CO2 it is usually expressed as parts per million, abbreviated as ppm. For CH4 model fraction is usually expressed in parts per billion (ppb). Mole fraction in (dry) air is used because it is a conserved quantity: it does not depend on the pressure, temperature, water vapor or condensed water content, which are all highly variable.
MSC - Meteorological Service of Canada (now Environment Canada).
NDVI - Normalized Difference Vegetation Index. A measure of vegetation greenness derived from AVHRR observations.
NEE - Net ecosystem exchange. The final balance of carbon surface exchange by an ecosystem, after accounting for photosynthesis, autotrophic and heterotrophic respiration. NEE = NPP - Rh.
NPP - Net primary production. Gross primary production (fixation of carbon via photosynthesis) minus autotrophic respiration (release of CO2 by the same plant).
pCO2 - The partial pressure of carbon dioxide. Contribution of CO2 to the total atmospheric pressure. Often the amount of CO2 dissolved in seawater is expressed as pCO2, since differences between atmospheric and oceanic pCO2 imply a disequilibrium that will drive a net exchange of CO2.
PgC/yr - petagram of carbon per year. A unit of emission equal to 1x1015 grams of carbon released per year. Technically, this is not a flux, since flux has dimensions of mass per unit area per unit time. The carbon dioxide emission is larger than the carbon emission by the ratio of molecular mass of CO2 to the atomic mass of carbon: 44/12.
Posterior Flux Estimate - The final estimate of emissions and sinks resulting from the assimilation process. Should be in optimal agreement with observations and estimates of fluxes coming from prior information.
Prior Flux Estimate - A first guess of emissions and sinks that is based on best available estimates from models or observations. Revisions to these first estimates will be tested against atmospheric observations and revised as a result of the assimilation process.
Posterior Uncertainty Estimate - The final estimate of uncertainty of fluxes resulting from the assimilation process. Use of atmopsheric observations will result in posterior uncertainty estimates that are reduced from prior uncertainty estimates.
Prior Uncertainty Estimate - An estimate of how uncertain prior fluxes are likely to be. The larger the uncertainty, the less importance the prior flux esimates will have in determining the final flux estimates.
ppb - The mole fraction is defined as the number of molecules of an atmospheric trace species in any given air parcel divided by the total number of all molecules (except water) in that parcel. For CH4 it is usually expressed as parts per billion, abbreviated as ppb.
ppm - The mole fraction is defined as the number of molecules of an atmospheric trace species in any given air parcel divided by the total number of all molecules (except water) in that parcel. For CO2 it is usually expressed as parts per million, abbreviated as ppm.
Q10 - Coefficient for describing the temperature dependence of heterotrophic respiration. Microbial respiration--the breakdown of organic carbon into CO2--is often modeled as an increasing function of temperature.
Regularization - Use of additional information to constrain parameter estimation and avoid overfitting of observations. An example would be to introduce a constraint that fluxes are zero during winter time in the Arctic, thus reducing the degrees of freedom of the system to be solved.
Residuals - The differences between the posterior simulated atmospheric trace species and observed mole fractions. Ideally they should be unbiased and have normal distributions.
Rh - Heterotrophic respiration. Conversion of organic carbon compounds into CO2 by microbial processes. "Heterotrophic" refers to the fact that the agent doing this conversion is distinct from the plant which created the organic carbon compound via photosynthesis.
Sink - Any process by which an atmospheric chemical species is removed from the atmosphere. Sinks may be natural (e.g., uptake of CO2 by photosynthesis and reforestation) or due to human activities (e.g., uptake of CO2 via managed forests and other carbon sequestration strategies).
Source - Any process by which an atmospheric trace species is added to the atmosphere. Sources may be natural (e.g., CH4 emitted by wetlands) or due to human activities (e.g., CH4 leaked to the atmosphere by natural gas pipelines or landfills).
TgCH4/yr - Teragram of methane per year. A unit of emission equal to 1x1012 grams of methane released per year. Technically, this is not a flux, since flux has dimensions of mass per unit area per unit time.
Time Series - Observations of a quantity taken regularly over time. An example of a well-known time series is the Keeling curve, representing CO2 concentrations at Mauna Loa, Hawaii from 1958 onwards.
TM5 - Transport Model, version 5. An off-line model of global atmospheric tracer transport. Uses meteorological driver fields from meteorological analysis models to model the advection and diffusion of atmospheric gases. Supports two-way nested grids to provide higher-resolution simulations over certain areas of the globe. See http://www.phys.uu.nl/~tm5/.
TransCom 3 - A special project of the International Geosphere-Biosphere Programme (IGBP), Global Analysis, Interpretation, and Modeling (GAIM) Project, the objective of which was to quantify and diagnose the uncertainty in inversion calculations of the global carbon budget that result from errors in simulated atmospheric transport, the choice of measured atmospheric carbon dioxide data used, and the inversion methodology employed. See http://www.purdue.edu/transcom/.
Uncertainty Estimates - CarbonTracker's fluxes are statistical quantities, which have associated "error bars". These error bars are expressed as estimates of a confidence interval. Generally, we report the standard deviation of the flux estimate as the uncertainty; this means that we believe that there is a 68% probability that the unknown, true flux lies within one standard deviation of our best guess flux.